Power transmission belt and method of making same

ABSTRACT

A method of making a belt including the steps of: (a) helically wrapping a fabric strip of predetermined width on a mandrel at a first helix angle; (b) helically winding a tensile cord onto the mandrel over the fabric at a second helix angle less than the first helix angle; (c) wrapping a sheet or a strip of elastomer material around the mandrel over the tensile cord; and (d) curing the elastomer material under pressure to form a belt sleeve. The mandrel may be grooved for making toothed belts. The fabric strip may be preformed. A resulting toothed belt has a fabric seam spanning several teeth and having a helix angle. The seam may be joined.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to an endless power transmission beltwith wear-protecting reinforcing fabric or jacket on at least onesurface, more particularly to an endless toothed belt with a fabric onthe tooth side which has a seam extending over more than two teeth, andto a method of making the same involving helically-wrapping a continuousfabric strip.

2. Description of the Prior Art

Representative of the art of toothed power transmission belts andmethods of making the same is U.S. Pat. No. 4,235,119 to Wetzel. Wetzeldiscloses three known methods of manufacturing toothed belts includingthe extruded tooth method, the tooth preform method and the flow throughmethod. All methods disclosed therein use a sheet of fabric wrapped on amandrel (i.e., a grooved cylindrical mold) with the ends of the fabricsewn together or otherwise united in a butt joint or lap joint, whetherthe fabric is square woven, bias-cut, stress-relieved, or stretchable.The sewn fabric sleeve or tube is often called a “jacket” and the jointmay be called a “splice.” The butt joint is preferably (according toWetzel) located over the ridges between the grooves in the outercircumference of the mold. As illustrated in FIG. 1, the jacket becomesthe tooth cover 12 for the teeth 18 in the finished belt 10, with thebutt joint 15 located preferably (according to Wetzel) in a land region19 of the belt, i.e. the thin section between two teeth. Belt 10 alsogenerally includes one or more tensile cord 16 spirally wound andelastomeric belt body 14 which fills out the teeth and surrounds thetensile cord. The flow through method includes placing the fabric tubeon the mandrel, spirally wrapping the cord onto the fabric, wrapping alayer of rubber onto the cord layer, then curing under pressure so thatthe rubber flows between adjacent cords to fill out the teeth, pressingthe fabric into the mandrel grooves. Joining or uniting the fabric endsis necessary so that the jacket stays in place on the mandrel during thecord winding step, which generates centrifugal forces that can cause thejacket to expand.

Also representative of the art of toothed power transmission belts andmethods of making the same is U.S. Pat. No. 3,756,091 to Miller. Millerdiscloses that there is a tendency for those splices of the jacket whichlie entirely in the root and land area of a belt tooth to break in usecaused by the reduced strength of the jacket. To eliminate this problem,Miller teaches, as illustrated by belt 20 in FIG. 2, that the jacket 12should be bias cut so that the minimum angle that splice 25 makes withthe belt side is such that if the splice starts at the point where theroot 22 of a tooth 18 blends with its land area 19 it will end, whenviewed in cross section, at the equivalent blend point on the other sideof the same tooth, and preferably, as shown, the splice 25 is at such anangle that the splice spans two teeth 18.

Herein, the sewn fabric splices illustrated in FIGS. 1 and 2 will bereferred to as “transverse” and “bias” splices or joints, respectively.A transverse splice runs from one side of the belt to the other side ofthe belt generally within the space of a single tooth pitch, although itmay wander more than that if not carefully aligned during building. Thebias splice of FIG. 2 typically might make an angle with the belt edgeof about 45° and span one or two tooth pitches. Conventionalsplice-joining methods for a sheet of fabric include sewing, fusing,laminating, bonding, and the like, and the joining step can be difficultto carry out without folds, gaps, or other potential defects. Thesesplices are generally considered weaker than the rest of the fabric, andthe tooth or land in which the joint resides may be the weakest portionof the belt to certain stresses. The bias splice and transverse splicecan both also result in a lot of wasted material. Splicing also is alabor intensive operation. It is currently generally preferred in theart to have a transverse jacket splice which is located in and followsalong the tip of a single tooth (contrary to Wetzel's teaching mentionedabove). Such splice location is difficult in practice.

U.S. Pat. No. 4,395,298 to Wetzel, et al., U.S. Pat. No. 4,444,621 toMarsh, et al., and U.S. Pat. No. 5,421,927 to Macchiarulo, et al.,disclose methods for making long length toothed belts based on firstforming a tubular sleeve comprising cover fabric, helically wrappedtensile cord, and elastomeric belt body material, then spirally cuttingthe sleeve to make a continuous strip of toothed-belt material,helically wrapping the strip around two wrapping drums which align theteeth and control the belt length, and fusing the adjacent loops ofhelically wrapped strip to form a new, longer belt or tubular sleeve. Asa result of this helical cutting and wrapping process, the toothed beltexhibits a cover fabric structured in the form of a narrow continuousstrip forming loops disposed in side-by-side relation and mating at therespective opposite edges. Marsh, et al., teaches that the helix angleof the spiral cut should be in the approximate range of 0.1 to 0.5degrees, to provide a strip width in the approximate range 5 to 20 mm.The cutting angle is approximately equal to the helical angle of thetensile cords. This small angle is necessary to prevent or minimizecutting of the cords, which would reduce the tensile strength of theresulting belt.

SUMMARY

The present invention is directed to systems and methods which providean endless power transmission belt with a fabric strip covering thesurface which is in contact with the pulley in which there is a helicalseam extending over more than two teeth and with the strip widthpreferably equal to or greater than the belt width. Thus, the belt needhave no transverse- or bias-oriented fabric splice, eliminating theissues surrounding conventional splice location.

The invention also relates to a method, process and materials formanufacturing an improved toothed belt having a fabric on the toothprofile, tensile cord reinforcement and elastomeric belt body.

The invention relates to the use of a continuous, fabric strip helicallywrapped around the profile mandrel (cylindrical grooved mold) in singleply or overlapping manner. The strip may be preformed to fit the profileof the mandrel. Thus, the seam is distributed over more than two teeth,or over several or many teeth, thus avoiding the weakening of the toothshear strength of any one tooth. Moreover, the construction methodpermits the splice helix angle to be independent of that of the tensilecord. In addition, this invention may reduce the cost for preparing thefabric as a tooth cover and reduce the number of steps required inmaking the toothed belt.

The invention relates to a belt having an elastomeric belt body, ahelically wrapped fabric strip covering a belt surface with adjacentedges of the fabric strip describing a helical seam which extends overmore than two belt teeth, or at least over three or more tooth pitches.The seam is preferably not overlapped, just butted. The seam may make afirst helix angle relative to a side edge of the belt. There may be ahelically wrapped tensile cord embedded in the belt body with thetensile cord describing a second helix angle relative to a side edge ofthe belt, with the first helix angle greater than the second helixangle. The first helix angle may be greater than the second helix angleby a factor of at least about two. The tensile cord lies in a singleplane, i.e., constant radial distance from the belt center. The belt maybe in the form of a toothed belt with the fabric strip covering thetooth profile surface of the belt. The seam helix angle may be in therange of about 1.5 degrees to about 19 or 20 degrees.

The fabric may be a stretch fabric or semi-stretch fabric. The fabricstrip may have a width equal to or greater than the width of thefinished belt, or in the range of at least about two times the width ofthe finished belt, or from about one to four times the width of thefinished belt. The seam may advantageously extend helically from onefourth to once around the circumference of the belt.

The invention is also directed to a method of making a belt includingthe steps of: (a) helically wrapping a fabric strip of predeterminedwidth on a mandrel at a first helix angle; (b) helically winding atensile cord onto the mandrel over the fabric at a second helix angleless than the first helix angle; (c) wrapping a sheet of elastomermaterial around the mandrel over the tensile cord; and (d) curing theelastomer material under pressure to form a belt sleeve with teeth. Thefabric strip may be a treated fabric. The fabric strip may be preformedand the mandrel grooved, resulting in a toothed belt sleeve. The beltsleeve may be cut into individual belts which may be further processed,for example, by grinding, printing, trimming, etc.

The method may include preforming the fabric strip so that teethcorrugations are oriented at a tooth angle with respect to an edge ofthe fabric strip, and the tooth angle may be complementary to the firsthelix angle. The fabric strip may have a width equal to or greater thanthe width of the finished belt, or in the range of about one to fourtimes the width of the finished belt.

According to an embodiment of the invention, the fabric strip may behelically joined to form a helically spliced jacket. According to anembodiment of the invention, the method of making the belt may includecontinuously joining, for example by sewing, gluing or welding, theedges of the fabric strip as it is helically wound to form a tubularsleeve or jacket. The method may include treating, drying, and the like.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe spirit and scope of the invention as set forth in the appendedclaims. The novel features which are believed to be characteristic ofthe invention, both as to its organization and method of operation,together with further objects and advantages will be better understoodfrom the following description when considered in connection with theaccompanying figures. It is to be expressly understood, however, thateach of the figures is provided for the purpose of illustration anddescription only and is not intended as a definition of the limits ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form part ofthe specification in which like numerals designate like parts,illustrate embodiments of the present invention and together with thedescription, serve to explain the principles of the invention. In thedrawings:

FIG. 1 is a partially fragmented perspective view of a prior art toothedbelt;

FIG. 2 is a partially fragmented perspective view of another prior arttoothed belt;

FIG. 3 is a partially fragmented perspective view of a toothed beltaccording to an embodiment of the invention;

FIG. 4 shows process steps according to an embodiment of the invention;

FIG. 5 shows an apparatus used in a processing step according to anembodiment of the invention;

FIG. 6 shows a partial plan view of a toothed belt according to anembodiment of the invention;

FIG. 7 shows a transverse section view of a toothed belt according toanother embodiment of the invention; and

FIG. 8 shows process steps and apparatus according to another embodimentof the invention.

DETAILED DESCRIPTION

FIG. 3 shows a toothed belt according to an embodiment of the invention.Belt 30 has an elastomeric belt body 14 with teeth 18 on one side.Embedded in belt body 14 is a tensile layer of spirally wrapped tensilecord 16. Tooth cover 32 is a strip of reinforcing fabric helicallywrapped around the belt and covering the tooth profile surface of thebelt. As a result of the process of wrapping the fabric strip, toothcover 32 has seam 35 extending longitudinally, or substantiallylongitudinally, in the belt circumferential direction, across manyteeth, and at a helix angle with respect to a side edge of the belt.Seam 35 is preferably a butt joint, but it could instead be a lap jointprovided the lap is half the width of the fabric strip. If the lap lessthan half the width, there will be sections having only one layer offabric under the cord line, resulting in some cords being at lower planethan others. If the lap is more than half the width, there will besections with three layers of fabric and portions of the cord on ahigher plane than others. Preferably the cord is uniformly located allin the same plane in any cross sectional view of the belt. Seam 35 asshown spans more than the eleven teeth shown in FIG. 3. By “seam” ismeant the line where the edges of two sections of fabric join or meet. Aseam need not be sewn or welded, but may simply be held by the materialforming the body of the belt. A seam may be “open” somewhat exposingsome of the tooth elastomer to view. An open seam may, for example, beopen up to one or two mm without detriment to the belt performance.

The tooth cover 32 according to the invention is a continuous strip offabric. Any type of fabric suitable for covering a belt surface may beused. For example, the fabric may be a woven, a non-woven, a knit, orthe like. The fibers of the fabric may be synthetic or natural orblends, including for example, nylon, polyester, acrylic, cotton,aramid, PEEK, or the like. The fabric may be treated in any way suitablefor treating tooth covering fabrics. For example, the fabric may becoated with an adhesive composition such as an RFL(resorcinol-formaldehyde-latex formulation), a rubber cement, or thelike. The fabric may be further coated on one or more sides with othercoatings for various purposes, such as friction modifying materials,rubber layers, or the like. The fabric may comprise a lamination of alayer of thermoplastic film on one side of a fabric. The term “fabric”is used herein to refer to a fabric whether so-treated or not, providedit is made ready for use in a belt manufacturing process.

By continuous strip is meant a piece of fabric that is very much longerthan its width. Preferably it is at least long enough to completelycover a belt mold when spirally wrapped thereon. Preferably it is of apredetermined width which is chosen to provide a predetermined helixangle when spirally wrapped on a belt mold. The helix angle of thefabric strip is a function of the width and the mold (or belt) diameter(or circumference). Preferably the predetermined width of the stripprovides for a helix angle that is greater than the helix angle of thesubsequently spiraled-on tensile cord, for example, more than twice thehelix angle of the cord, or equivalently, the width of the strip may bemore than twice the width of the cord. If two cords (e.g. S and Ztwisted cords) are spiraled on side by side, it is preferable that thehelix angle of the strip be more than twice the helix angle of a cord,or that the width of the strip be more than four times the width of acord. Thus, the longitudinal sheer plane of the seam will not align withthat of the tensile cord layer, preventing any new weakness along thelength of the belt.

Preferably the width of the fabric strip is wider than the finished beltwidth, so that no more than one longitudinal seam will be located acrossthe width of the belt at any location in the belt. According to anembodiment of the invention, the fabric strip may have a predeterminedwidth equal to or greater than the width of the finished belt, or in therange of about one to four or five times the width of the finished belt,or from one to three times the width of the belt, or about twice thewidth of the belt. According to another embodiment of the invention, thewidth of the strip may provide for a seam helix angle relative to thebelt edge in the range of from 1.5 degrees to about 20 degrees, or from2 to 18 degrees. Preferably the helical fabric seam spans more than twoteeth, for example more than four teeth, or preferably more than six oreight teeth. Preferably the helical jacket splice does not extend morethan once around the belt circumference. Preferably the helical fabricsplice may extend around the belt in the range from about one fourth toabout one half the belt circumference. If the fabric width is less thanthe width of the belt, there will be a seam extending more than oncearound the belt circumference, which could result in a weakening of thebelt. Also, if the fabric width is less than the width of the belt, morewraps are required to cover the mold than with wider strips, resultingin longer process times than desirable.

FIG. 7 shows another embodiment of the invention having two layers offabric and a single spiral splice. Thus, in FIG. 7, belt 70, havingelastomeric body 14 with teeth 18 and embedded tensile cord 16, hassplice 75 involving two layers of jacket. As before, the jacket is acontinuous strip that is helically wrapped or spiraled onto a belt mold.However, the spirals overlap about half the width of the strip, so thatone spiral layer of fabric 76, has second spiral of fabric 74 partiallyoverlapping layer 76 and partially forming an adjacent first layer offabric which is in turn overlapped by the next spiral layer 72. In aconventional process with more than one sheet of fabric with ends joinedacross the mold face, there will be a transverse splice for each layerof fabric. Care is usually taken to ensure that the two splices arestaggered. The two-layer embodiment of FIG. 7 only has one seam 75, withthe advantages resulting from being spread across multiple teeth andalong the length of the belt instead of transverse. Overlapping thespirals about half the fabric strip width provides a most uniformtwo-layer fabric cover and provides a uniform support for the cord.

Whether one or two layers of fabric are used in the belt, it ispreferable that the resulting jacket layers are of uniform thickness tosupport the cord layer at a uniform position in the belt. In otherwords, the seam should either be a butt joint without any overlap or beoverlapped half the fabric strip width to provide a uniform double layerof fabric as illustrated in FIG. 7. Thus, the cord centerlines should becollinear when viewed in section as in FIG. 7, with no cords higher orlower than any other cords. In terms of the cord winding on the mandrel,the cords should be at a constant and uniform radius from the center ofthe belt or mandrel.

Conventional toothed belts have typically a sheet of fabric on the toothprofile to reinforce the tooth and protect against wear. These fabricsare designed with a stretch in the range of 30% to 80% or even more inthe circumferential direction of the belts. The stretch is needed forprocessing reasons to allow forming of the teeth with the elastomericmaterial, for example in the conventional flow-through process.Alternative methods use a preformed sheet of fabric with a low-stretchor semi-stretch fabric, i.e. less than 30% stretch or less than enoughstretch to go from a circle on a mold to following the tooth profile. Inboth cases, the preparation of the fabric as a sheet the full width ofthe mold or mandrel prior to the molding process is time consuming andresults in material waste. Also, the conventional methods result in afabric splice that is essentially parallel to the belt teeth and maysometimes be considered a weak point in the product which can limit itsservice life and may provide a source of undesired noise.

On the other hand, embodiments of the present invention include the useof a continuous preformed fabric strip wrapped around the profilemandrel in a single ply. Thus, the present invention provides anapproximately longitudinal seam which spans many teeth, but represents aminimal disruption to the surface of any one tooth. Therefore theinventive belt splice does not provide a localized noise source, or aweakened tooth. In addition, the cost for preparing the fabric as ajacket may be reduced, and the steps in making the toothed belt may bereduced or made easier to carry out.

The elastomer may be any suitable elastomer for forming a belt body. Forexample, the elastomer may be rubber, thermoplastic elastomer,thermoplastic polyurethane, cast polyurethane, or the like. Rubberelastomers may be based on any suitable rubber composition, such asstyrene-butadiene rubber (SBR), polychloroprene, natural rubber, nitrilerubber (NBR), hydrogenated NBR or SBR, ethylene-alpha-olefin elastomers,acrylic elastomers, butyl, ethylene vinyl-acetate elastomers, and thelike, and blends thereof. Any suitable combination of ingredients may beincluded in the elastomer, such as curatives, extending fillers andoils, reinforcing fillers and fibers, process aids, antidegradants,plasticizers, and the like. An advantage of the present invention isthat elastomers of different types and/or properties may be plied upwith greater control and variety than in the conventional flow-throughprocess. Thus, for example, the belt body may include one type ofelastomer in the preformed tooth, and/or another elastomer compositionaround the tensile cord, and/or another elastomer composition over thecord on the back of the belt. A second fabric or jacket could also beapplied to the back side of the belt, either by helical wrapping a stripof fabric as described herein, or using a sheet of fabric.

The cord may be any suitable tensile cord for toothed beltreinforcement. For example, the cord may comprise fibers of glass,aramid, carbon, polybenzobisoxazole (PBO), polyketone, boron, metalwire, or the like, or combinations thereof. The cords may be of anysuitable construction, such as twisted, folded, cabled, core-sheath, orthe like. Two cords constructed of opposite twist may be used, spiraledin the belt side by side, resulting in alternating cords of oppositetwist. The cords may include one or more adhesive or protectivetreatments, such as primers, dips, RFL, overcoats, rubber cements, orthe like. An advantage of the present invention is that the cord spacingmay be reduced compared to the conventional flow-through process.

The tooth profile may be any suitable tooth profile. For example, thetooth profile may be trapezoidal, curvilinear, truncated curvilinear, orthe like.

The invention also relates to a method for manufacturing endless beltshaving a fabric on an external surface. The method is particularlyuseful for making toothed belts having a fabric covering the toothprofile surface. FIG. 4 illustrates key steps in the manufacture oftoothed belts according to an embodiment of the invention. FIG. 4 showsmandrel 40 with grooves 42 shaped to produce a desired tooth profile.Fabric strip 43 of width “w” is shown being spiraled onto mandrel 40from right to left at helical angle “α”. Fabric let off 44 isrepresentative of any suitable apparatus for applying the fabric stripat an appropriate feed rate, tension, cross head speed, etc., as themandrel rotates. The spiraling of fabric 43 results in helical seam 45.In FIG. 4, the fabric is applied so that each subsequent loop of fabricbutts against the previous loop, forming a helical butt splice. In otherembodiments, the wrapping process may overlap the fabric half its widthto form a double layered jacket in the belt, as illustrated in FIG. 7.The strip width must be less than the face width of the mandrel in orderto consider the strip to be spiraled onto the mandrel and to avoidfabric waste. Preferably the fabric strip is wrapped around the mandrela plurality of times, although the number of wraps will depend on themandrel width and the strip width. The preferred fabric dimensions andhelical angles discussed above apply here as well.

After fabric strip 43 is applied to the mandrel, FIG. 4 shows tensilecord 46 being spiraled from a cord let off 47 onto the mandrel, againfrom right to left. Thus, cord layer 48 may be formed on top of thefabric layer. Instead, the cord could be applied from left to right, orin the opposite direction as the fabric spiral. A pair of cords of equaland opposite twist may be used instead of a single cord. A plurality ofcords may likewise be applied. Since the cord is much thinner than thefabric width, the helical angle of the cord will be much less than thatof the fabric, preferably less than half of a. A layer of elastomercould be applied over the fabric before winding on the cord, either as abutt joined sheet or as a spiraled strip.

After cord layer 48 has been applied, a layer of elastomeric material iswrapped around the cord layer, either as a butt-joined sheet or as aspiraled strip. Multiple elastomer layers could be applied, for example,an adhesion layer next to the cord and another layer for the backside ofthe belt. The material may then be cured in any suitable vulcanizationor cure process, typically under heat and pressure. The pressure forcesair out from between the cords and layers and forces the elastomer intothe spaces between and around the cords. The resulting tubular object isoften referred to as a sleeve of belts or a belt sleeve. The belt sleevemay be further processed in any way desired, including, for example, oneor more of cutting a number of individual endless belts therefrom,applying or printing a label, trimming an edge, grinding to a desiredbelt thickness, and the like.

Preferably, fabric strip 43 may be preformed to the general shape of themandrel grooves before the strip is spiraled onto the mandrel.Preforming has a number of advantages. The preformed strip, whichfollows closely the contour of the mold, is less prone to rubber orelastomer flowing through the splice during the curing or molding of theelastomer belt body. Preformed jacket can utilize a wider variety offabrics, including for example, non-stretch or semi-stretch fabrics.Fabrics with less stretch than required for the conventional flowthrough process may offer better tooth reinforcement, and may be moreeconomical, for example. Conventional methods utilizing preformed sheetsof fabric are complicated by the need to join the edges to make ajacket. With a preformed strip, no edge joining is needed.

Any suitable fabric preforming process may be used to preform the fabricstrip. One method of preforming may be carried out directly on the moldor mandrel. The fabric strips may be wound directly onto the mold usinga profiled roll which pushes the fabric into the tooth-forming groovesof the mandrel. The fabric may be held in place on the mold with atemporary adhesive, or by fixing the fabric strip in the preformedcondition with one or more thin yarns or retaining threads wound orspiraled on the outside of the strip during the strip winding operation.The thin yarns may be left in place or removed as the cord is spiraledonto the mold. In addition or instead, elastomer tooth material may beforced into the tooth-forming grooves to hold the fabric shape. Anysuitable tooth elastomer material may be used, and it may be differentfrom or the same as the belt body elastomer.

Another method of preforming the fabric strip is illustrated in FIG. 5.Fabric strip 50 is first fed between two profiled rolls 51 and 54.Secondary profile roll 54 has teeth 55 which push fabric strip 50 intotooth-forming grooves 52 of primary roll 51. The fabric strip is thusmade a corrugated strip 60, which might then be used on the mandrel forbuilding belts. Preferably, an additional operation is applied to thecorrugated strip to improve retention of the corrugated shape duringwinding onto the mandrel. One alternative is to apply a formableelastomer to fill the tooth corrugations of the fabric strip. FIG. 5shows elastomer strip 62 fed between press roll 64 and primary roll 51to make preformed fabric strip 43. Elastomer strip 62 may be anysuitable elastomer material as described above for the belt body,including the same or a different material as used for the belt backside in a subsequent belt molding step. Also, the two profile rolls 51and 54 may have grooves of such size and pitch and with a groove helixangle adequate to produce a tooth helix angle in the preformed profile,matching exactly and being parallel to the profile of the moldingmandrel. In this case the angle of the teeth on the preformed strip withrespect to the edge of the strip is complementary to the helix angle ofthe strip itself when wrapped onto the mandrel. By complementary ismeant the two angles together make a right angle. FIG. 6 illustratestoothed belt 60 with alternating teeth 18 and lands 19 and fabric seam65 oriented at an angle, α, with respect to side edge 63. Seam 35 isalso oriented at an angle, β, with respect to teeth 18. Angles α and βare complementary. Seam 65 spans about seven belt teeth in FIG. 6.

The invention can improve a toothed belt in a number of aspects. Thefabric seam is at least distributed over many teeth, which eliminatesthe weak spot caused by a typical splice being parallel to the tooth orover just two teeth. The seam on the inventive belt is approximatelyparallel to the usual stresses on the belt teeth, so that the stressesdo not tend to open up the seam.

The preforming operation allows the use of different elastomericmaterials for the tooth profile and for the backside of the belt. Aharder tooth material can improve the load capability whereas thebackside material may be softer to reduce noise or optimize the desiredfriction characteristics. In addition, preforming allows the option ofadding a layer of elastomer and/or fibrous material over the fabric andunder the cord, for example, to adjust the cord pitch line, enhanceadhesion, and the like. Unlike prior preform processes, the inventiveprocess can completely fill the tooth with rubber, or overfill the toothwith rubber to support the cord evenly all around the mandrel, includingover the grooves.

The preforming of the teeth avoids the conventional flow-through processof toothed belt manufacture. Choice of tooth material in that process islimited because the material needs good flow properties to get throughthe cord layer and because of the need to prevent wiping off of theadhesion coating on the tension members. The flow-through method alsorequires a certain proportion of gaps between the tension members,restricting the number of tension members. As the product made by theinvention does not need the flow-through, the belt can have more tensionmembers per unit width allowing a narrower belt to have the samestrength.

The continuous fabric strip can be woven or knit to the desiredpredetermined width, avoiding trim waste and allowing fabricconstructions of significantly higher strength, improved wear and noisecharacteristics and flexibility. The fabric strip can be applied in theweave direction, i.e. with the weave direction oriented around the belt.Conventional techniques with sheet fabric generally require the fabricwidth direction oriented around the belt, requiring the fabric to be cutand rotated, often with more than one splice.

In the flow-through process, the rubber may distort the cords duringflow, in particular by pushing the cord segments which span a moldgroove down somewhat into the groove. This may result in poordimensional stability and/or local flex fatigue problems in the cord. Bypreforming the fabric and filling or even overfilling the tooth profileof the fabric with elastomer material, the cord can be given supportacross the mold grooves during cord winding, resulting in a morecircular cord path, better length stability, and/or improved flexfatigue. Thus, preformed fabric can insure that the tension member isnot deflected between the teeth during cord winding (a chordal effectthat results in a cord bend radius smaller than the mold radius) thusavoiding damage to the tension members and improving the belt elongationcharacteristics resulting in improved length stability. In other wordsby preforming the jacket strip with elastomer filling the teeth,according to an embodiment of the invention, the cord can be supportedon the entire circumference of the grooved mold during cord winding, anideal cord winding situation.

According to another embodiment of the invention, the helical “seam”where the edges of two sections of fabric join or meet may be joined,for example by sewing, gluing, fusing, taping or welding. A loosely sewnseam may be “open” somewhat, exposing some of the tooth elastomer toview. FIG. 8 illustrates apparatus and process 80 for joining a treatedfabric strip in a helical manner to form a fabric sleeve. In FIG. 8,fabric strip 43 is fed in the direction indicated by arrow 81 through anoptional fabric treatment dip tank 82. Dip tank 82 and guide rolls 84are shown for illustrative purposes only, and may be any appropriatecombination of treating apparatus, for example rollers, squeeze rolls,wipers, sprayers and the like may used to treat the fabric, includingmultiple treatment stages, such as primer, RFL, final coat, and thelike. Treated fabric may then be passed through a suitable drying stageor dryer, such as oven 86 in FIG. 8. Any suitable treatment may be usedas described previously. Fabric strip 43 may then be fed over suitableguide rolls 88 onto guide bars 90 where the fabric is helically wrappedwith edges abutting in to form helical seam 96. Seam 96 is joined byjoining machine 92, which is illustrated as a sewing machine with foot94. The joining machine may operate on the top or the bottom portion ofthe sleeve, or from the inside or outside of the sleeve. The joiningmachine may utilize any suitable joining method, such as ultrasonicwelding, thermal welding, laser welding, gluing, sewing, stitching, useof reinforcing fabric tape, or adhesive film, or other suitable joiningmaterial, or the like, to seal and reinforce the seam. The strip isjoined continuously as it is fed onto the guide bars resulting in atubular fabric sleeve growing lengthwise in the direction of arrow 98.Although joining machine 92 is shown stitching the seam from the insideand bottom of the sleeve as a nonlimiting example, it should beunderstood that the stitching, welding, or joining could be from the topor outside of the tube, or any other suitable configuration for theprocess used to join the seam. The tube may be cut in lengths to make ahelically spliced jacket to fit a mold or mandrel such as mandrel 40.The jacket may be of stretch fabric, applied to a mandrel for building abelt sleeve according to the flow-through method or other knownbelt-making method using spliced jackets. The advantages of this methodover conventional transverse-splice methods include that the helicalsplice requires no special care to locate it, the cutting of the jacketinvolves almost no material waste, the width of the fabric strip is usedas-woven without cutting, a number of conventional jacket process stepsmay be eliminated and/or combined into a single continuous operation fortime, labor and cost savings, and the like. The guide bars 90 may haveadjustable spacing for making helically spliced jackets of any desiredcircumference. Guide bars 90 may be cylindrical and may, but need not,rotate.

The helically joined jacket may be of a stretch fabric for toothformation by the flow through process of toothed belt makingAlternately, the fabric may be stretch or semi-stretch and the teeth maybe preformed as the jacket is applied to the mandrel. Preforming may useany suitable technique or combination of techniques, including pleatingor forming by means of toothed wheels, vacuum forming, retainingthreads, inserting tooth rubber, and the like. The jacket sleeve may bemade larger than the mandrel to accommodate formation of the toothprofile on the mandrel within the stretch limitations of the fabric.

It should be understood that, in addition to endless toothed belts, thisinvention is also applicable to fabric reinforcements for the backsideof the belts, for flat belts, dual-sided toothed belts, and also formulti-V-ribbed belts and V-belts. It is also applicable to belts builtinverted on the mandrel with a fabric layer resulting on the backside ofthe finished belt. It is also applicable to helical-toothed belts,having transverse teeth that are at an angle other than perpendicular tothe sides of the belt, and/or also applicable to toothed belts withteeth that are not straight, but curved. It is also applicable to anyother shaped tooth or toothed belt such as helical teeth, teeth in aherringbone design, or oblique and offset teeth, or the like.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions, andalterations can be made herein without departing from the scope of theinvention as defined by the appended claims. Moreover, the scope of thepresent application is not intended to be limited to the particularembodiments of the process, machine, manufacture, composition of matter,means, methods, and steps described in the specification. As one ofordinary skill in the art will readily appreciate from the disclosure ofthe present invention, processes, machines, manufacture, compositions ofmatter, means, methods, or steps, presently existing or later to bedeveloped that perform substantially the same function or achievesubstantially the same result as the corresponding embodiments describedherein may be utilized according to the present invention. Accordingly,the appended claims are intended to include within their scope suchprocesses, machines, manufacture, compositions of matter, means,methods, or steps. The invention disclosed herein may suitably bepracticed in the absence of any element that is not specificallydisclosed herein.

What is claimed is:
 1. A toothed endless belt comprising: an elastomericbelt body with a plurality of teeth defining a toothed surface of saidbelt; and a helically wrapped fabric strip covering the toothed surfacewith adjacent edges of the fabric strip abutting one another describinga helical seam; with said seam extending over more than two teeth. 2.The belt of claim 1 wherein the fabric strip has a width equal to orgreater than the width of the belt.
 3. The belt of claim 1 wherein saidseam extends over more than four teeth.
 4. The belt of claim 1 whereinsaid seam extends at least one fourth of the circumference of the beltand no more than once around the circumference of the belt.
 5. The beltof claim 1 wherein said seam defines a first helix angle relative to aside edge of the belt; and further comprising: a helically wrappedtensile cord embedded in the belt body with the tensile cord describinga second helix angle relative to the side edge of the belt; with thefirst helix angle greater than the second helix angle.
 6. The belt ofclaim 5 wherein the cord centers are collinear when viewed in a beltsection.
 7. The belt of claim 6 wherein the first helix angle is greaterthan the second helix angle by a factor of more than two.
 8. The belt ofclaim 7 wherein the first helix angle is in the range of about 1.5degrees to about 20 degrees.
 9. The belt of claim 1 wherein the fabricis a semi-stretch fabric.
 10. A method of making a toothed endless belthaving an elastomeric belt body with a plurality of teeth defining atoothed surface of said belt comprising: (a) helically wrapping a fabricstrip of predetermined width on a grooved mandrel at a first helix anglewith adjacent edges of the fabric strip abutting one another describinga helical seam; with said seam extending over more than two teeth; and(b) helically winding a tensile cord onto said mandrel over said fabricat a second helix angle; (c) wrapping a sheet of elastomer materialaround said mandrel over said tensile cord; and (d) curing saidelastomer material.
 11. The method of claim 10 wherein said second helixangle is less than said first helix angle.
 12. The method of claim 10wherein said mandrel has a groove profile; the method further comprisingpreforming said fabric strip into a corrugated shape to fit the grooveprofile of said mandrel.
 13. The method of claim 12 wherein thepreforming results in the fabric strip having teeth corrugationsoriented at a tooth angle with respect to an edge of the fabric strip,and said tooth angle is complementary to said first helix angle.
 14. Themethod of claim 12 wherein the preforming includes filling the toothportions of the fabric strip with an elastomeric tooth material.
 15. Themethod of claim 10 wherein said curing includes heating said elastomermaterials under pressure to form a belt sleeve with teeth; and themethod further comprises cutting said sleeve to form a plurality ofendless toothed belts having a width.
 16. The method of claim 15 whereinthe predetermined width of the fabric strip is greater than the width ofthe belts.
 17. The method of claim 15 wherein the predetermined width ofthe fabric strip is from one to four times the width of the belts.
 18. Atoothed endless belt comprising: an elastomeric belt body with aplurality of teeth defining a toothed surface of said belt; a helicallywrapped tensile cord embedded in the belt body; and a helically wrappedfabric strip covering the toothed surface with adjacent edges of thefabric strip abutting one another describing a helical seam extendingfrom one side of the belt to the other side of the belt; with said seamextending over more than two teeth.
 19. The belt of claim 18 wherein thecord centers are collinear when viewed in a belt section.